Electric heating system



Feb. 9, 1937. R. H. PARK 2,070,491v

ELECTRIC HEATING SYSTEM Original Filed Dec. 12, 1931 2 Sheets-Sheet 1 Ira/710212222 RoZez iHPwrfi,

. diliiys Feb. 9, 1937. PARK 2,070,491

ELECTRIC HEATING SYSTEM Original Filed Dec. 12, 1931 2 Sheets-Sheet 2 I 3/06 21/350 2".- B02167; IlParZr,

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Patented Feb. 9, 1937 UNITED STATES PATENT OFFICE Divided and this application August 22, 1935, Serial No. 37,277

2 Claims. (01. 219 2o) This application is a division of my copending application which has eventuated in Patent No. 2,012,618.

This invention relates to electric heating, and

5 the object is to provide an improved mechanism wherein theobject to be heated, for example, a liquid-containing vessel, is included as a part of a circuit of high amperage and low voltage.

My invention will be well understood by reference to the following description of a single embodiment thereof, shown by way of example in the accompanying drawings, wherein:

v Fig. 1 is a wiring diagram corresponding precisely to that shown in Fig. 8'of the parent application; and

Fig. 2 is the same diagram, but omitting the motor and the motor magnet shown in Fig. 1, since the invention as herein broadly claimed is not limited to the employment of either of said parts.

Before referring specifically to the construction shown in the drawings, it is pointed out that in general, cooking vessels, whether sauce or frying pans, or for other purposes, as well as their contents, are subject to damage if overheated. Heretofore, such risk of overheating has been overcome by the use of internal fusible plugs and thermostatically operated switches for opening the circuit in response to an excess of temperature. However, fusible plugs must be renewed after every fusing occurs, which is inconvenient, and intemalthermostats are difilcult to construct and make reliable, especially in view of the limited space available. Moreover, the tempera- 35 tures at'which they operate are not readily sub- Ject to regulation, without a construction which permits water to penetrate to the heating elements, if the unit is submerged. This is important in the case of cooking vessels.

40 In general, the resistance of a heating element is a function of its temperature, and I have herein, disclosed an arrangement whereby the circuit supplying the heating element with current may be opened in response to such change.

45 Electric heating appliances for cooking purposes are commonly used wherein the heat is derived from a resistance wire heated to incandescence. While such heating elements are satisfactory for baking, broiling and the'like, they 50 -are'slow and uneconomical for such operations as boiling, and in the construction about to be described (see Fig. 1) a liquid-containing vessel 9, such as a sauce-pan, is included as a part of a circuit of high amperage and low voltage which I may be the secondary circuit of the transformer l3, of which the primary coils I! may be energized from a source of relatively high voltage, such, for example, as the ordinary 110 volt electric lighting mains. A current of high heating capacity is thus passed directly through the pan, 5 heating the liquid therein rapidly and efllciently. To exclude current from the contents of the pan with possible electrolytic action thereon I prefer to provide the pan with an enamel'lining. The bottom of the sauce-pan 9 maybe provided with 10 downwardly projecting, prong-like contacts I! which may be firmly engaged by clamping jaws i9 to connect the pan in the circuit.

Means, preferably power means, are utilized to close the clamps, and, after they are closed, to 15 initiate the current supply. When the heating operation is completed, the supply circuit is preferably opened and then the clamps are released.

I will first describe the operation in a general way with reference to the diagram, Fig. 1. 20

Referring, therefore, to Fig. 1, the pan 9 being placed in position with the contacts i1 between the open jaws i9 of the clamps to permit the latter to be closed thereon, the heating operation may be started by moving the double pole 25 switch 2i to the left in the figure to engage the contact 23. Current is thus supplied through wire 24 and bridge 25 to an electric motor 21 which by mechanical means (not shown in the diagram) closes the clamps l9. When the clamps are closed, movement of the motor initiates the flow of current to the transformer l3, and herein a cam 29 driven by the motor closes switch 3i energizing the solenoid 33. The core of this solenoid rising causes bridge to close the cir- 35 cult to the primary ii of the transformer. It also lifts bridge 25, breaking the circuit to motor 21, stopping the same, and lifts bridge 31 in the conductor leading to a motor magnet 39 so that the latter cannot receive current while the solenoid 40 is energized. The number of turns in the primary and consequently the rate of heating may be controlled in the usual manner by a controlling switch ii.

When the heating is completed, switch 2i is moved over into contact with the pole 43. By this means the circuit of solenoid 33 is broken and bridge 35 falls, interrupting the current to the primary i 5. As bridge 31' closes, current flows through pole 43 to the motor magnet 39, the operation of which provides for the release of clamps l9 and also for the reopening of switch 3i.

Although I have in Fig. 1 shown the motor 21 with cam 23 and switch 3|, and have also shown motor magnet 39, it is to be derstood that those Fig. 2 they have'been omitted. It is unnecessary therefore specifically to describe Fig. 2.

Referring again to Fig. 1, and also to Fig. 2, I have there shown means to open the heating circult in case, the resistance abnormally rises, as

might happen, for instance, when a boiling operation was in question and the pan boiled dry and became red hot. For this purpose I interpose in the circuit of solenoid 33 a safety switch which may comprise a fixed contact 99 with which cooperates a spring blade ill connected in the circuit by means of a flexible lead I03 and carried by a rocking beam I05 pivoted at ill! and having the spring I09 attached thereto through a suitable lever arm as shown so as to hold the beam tilted either in the closed position of the switch as shown or in the open position when the beam has rocked somewhat clockwise. A handle III on the beam provides for returning the switch to the closed position shown after it has been opened in the manner about to be described. Opposite ends of the beam arehere shown as connected to the cores of coils Iii and iii respectively, the conjoint action of which on their respective cores controls the position of the beam. Coil H3 is arranged in series in the circuit of the primary coils ii of the transformer and is so wound as to attract its core with a force proportional to the current (amperage) Coil 5, however, is of high resistance and may be bridged across a portion of the coil i5, conveniently with the addition of a resistor HT, and acts on its core with a force proportional to the electromotive force or voltage. Consequently when the resistance of pan 9 rises, the current demand of the secondary falls, current (amperage) in primary I! decreases, the electromotive force increases, and the force of coil 5 overcomes the force of coil H3, rocking beam "5 clockwise and opening the switch.

It will be seen that the safety switch 39-4,

the operation of which has just been described, is disposed in the lead from pole :3 of switch 2! before conductor 21 branches therefrom and conpended claims rather than to the foregoing description to indicate the scope of the invention.

1 claim:

1. In an electric cooking device in combination with a cooking vessel having a self-containing heating element, means for connecting the same in an electric circuit to a source of electric energy,

means for controlling in substantial degree the voltage supplied to the circuit whereby to control the rate of heat supply to the vessel, a switch controlling the supply of energy to the circuit, differentially acting means controlling said switch comprising an electro-magnetie motor device proportionately responsive to the voltage and an electro-magnetic motor device in a diiferent magnetic circuit proportionately responsive to the current whereby to open the switch on abnormal increase of resistance in the vessel- 2. In an electric cooking device in combination with a cooking vessel having a self-containing heating element, means for connecting the same in an electric circuit to a source of electric en ergy, means for controlling in substantial degree the voltage supplied to the circuit whereby to control the rate of heat supply to the vessel, a switch controlling the supply of energy to the circuit having self-maintaining on and off positions and manually movable from the latter to the former position, differentially acting means controlling said switch comprising an electromagnetic motor device proportionateiy responsive to the voltage and an electro-magnetic motor device in a different magnetic circuit proportionately responsive to the current whereby to move the switch to 01! position on abnormal increase of resistance in the vessel.

ROBERT H. PARK. 

